Satellite geolocation systems, called “GNSS” systems (Global Navigation Satellite System) are now very widely used in motor vehicles. These systems are more often than not incorporated in a navigation system which in turn comprises a set of global digital maps, then making it possible to guide a driver to the desired destination. Geolocation systems that can be cited by way of example are the North American GPS system (global positioning system), the Russian GLONASS system or the European GALILEO system.
Similarly, driving assistance systems have expanded in recent years, with a consequential improvement in road safety and driving comfort.
For example, the document US 20110106442 discloses a motor vehicle equipped with a collision avoidance system. This avoidance system is designed to process information received from a GPS appliance, from a motion sensor and from a device situated on the roadside and transmitting topographical information in order to predict the future trajectory of said vehicle. The system is thus configured to be able to provide warnings or undertake actions in order to avoid collision between said motor vehicle and other motor vehicles.
In order to detect, with a high level of confidence, a risk of collision between a “subject” motor vehicle and another, “target” motor vehicle, it is essential to have a relative positioning accuracy between the two motor vehicles of less than a meter. Now, a GPS appliance cannot position the motor vehicle with an absolute accuracy better than 3 to 5 meters, which is scarcely sufficient. Even if our GPS appliance were to be of the type that is coupled to a network of terrestrial stations (in which case the concept of “differential” GPS comes into play), the absolute positioning accuracy obtained would still be insufficient. In effect, the latter is of the order of 2 to 6 meters in Europe, and then only in good satellite transmission conditions. This is why the use, alone, of a satellite positioning system does not make it possible to sensitively detect the longitudinal alignment between two vehicles traveling on the same highway.